Bearing for wear detection

ABSTRACT

A bearing lined with silver, there being radioactive atom dopants of two species, neither of which need be silver, at a particular depth of the silver lining and a method of placing these radioactive atom dopants in said bearing by electrodeposition without altering the quality or bond strength of the silver lining.

United States Patent [191 Bardach BEARING FOR WEAR DETECTION [75] Inventor: Herbert Bardach, Danbury, Conn.

[73] Assignee: Avco Corporation, Stratford, Conn.

[22] Filed: Apr. 21, 1971 [2]] Appl. No.: 136,083

[4 1 Mar. 19, 1974 2,468,905 5/1949 Warren 250/106 T 2,621,988 12/1952 Donley 2,580,652 1/1952 Brennan 2,569,149 9/ l 951 Brennan 2.938.125 5/1960 Marak 250/106 T Primary Examiner-Charles J. Myhre Assistant Examiner-R. H. Lazarus Attorney, Agent, or Firm--Charles M. Hogan; Irwin P. Garfinkle [5 7] ABSTRACT A bearing lined with silver, there being radioactive atom dopants of two species, neither of which need be silver, at a particular depth of the silver lining and a method of placing these radioactive atom dopants in said bearing by electrodeposition without altering the quality or bond strength of the silver lining.

8 Claims, 4 Drawing Figures 42 viz/772% PAIENTEDHAMQIBM 3797.896

FIG. 2.

on In T* i b 22 I6 I Oil 8i Wear Particles Out 32 Detection Ot Radioactive Wear Particles Detector it fi -.5;

Oil Out flii FScintiliatiorTi Crystal 1 Engine With 1 L ES IPLJ Tagged Bearings \OH SGmDIe or a A Oil Filter 0 0' a A 42 i INVENTOR Herbert Bardach WWW BEARING FOR WEAR DETECTION This invention relates to silver lined metal articles subject to wear, such as antifriction bearings, and to such articles containing radioactive atom dopants placed at a desired sub-surface layer of the silver lining wear surface.

The provision of a radioactive material in a surface layer of bearings, pistons, cylinders, gears and other similar metal surfaces is disclosed in Ferris U.S. Pat. No. 2,315,845, as a means for determining wear in such surfaces in test apparatus.

Another means for detecting wear in tools, such as bits, is described in Warren U.S. Pat. No. 2,468,905. In that disclosure, a pocket or recess is provided in the tool and a radioactive capsule is inserted in the recess. When the tool face has worn down to the capsule, radioactive material begins to wear away and is detected as in the Ferris patent or by other suitable means.

Still another method for determining wear is described in Marak U.S. Pat. No. 2,938,125 in which a bearing surface is coated with a radioactive layer and this in turn is overlaid with a wear resistant layer.

The present invention is directed to an improvement over the prior art as it is exemplified in the above noted patents. In the present invention, an extremely thin layer of the silver lining at a desired sub-surface site situated beneath a wearing surface is provided with minute amounts of radioactive silver and/or radioactive irripurities without affecting the quality or bond strength of the silver lining. As a result, the antifriction bearing or other silver-lined article continues to function usefully and in the same manner as it had before the overlying non-radioactive layer had worn away while the wear particles generated as a result of the wear of the radioactive layer provide an indication to a detecting device that wear of the article has reached the depth of the radioactive layer.

I "rr'aisrereirea a555cm;asamsmaasaaitfiaafi oactive silver film is tagged with at least one radioisotope having a much longer half-life than the half-life of the longest lived radioisotope of silver, thereby extending the useful life of the detection period for the resulting silver lined article. A For examplefa silver-lined bearing is produced with an extremely thin layer of the silver lining being tagged with radioactive silver-110m and cobalt-60 at a depth at which the user is to be warned of the extent of wear. A layer of silver overlying the radioactive layer provides the layer to be worn away in service, and below the radioactive layer another layer of silver is provided so that the bearing can continue in service until the radioactive material worn away has been detected and until replacement of the bearing can be effected.

lt w ill be seen that the pr esent invention provides both technical and economic advantages over the prior art described above, especially in the manner in which it reduces the amount of radioactive material to a minimum and in the use of a radioactive material which does not impair the effective functioning of the device when the overlying layer is worn away.

One object of the invention is to provide metal arti cles having an outer layer of wearable metal with an underlying supporting structure which is radioactive and which enables the user of the article to detect when the article has worn to an extent requiring its replacement.

Another object is to provide a novel means for depositing a radioactivated silver film on an article, said film being tagged with a radioisotope whose half-life is considerably longer than the half-life of the longest-lived radioisotope of silver, whereby the useful life of the warning layer is extended.

Still another object of the invention is to provide minute amounts of a secondary radioisotope species in the bearing silver lining so that the point of bearing wear can be identified, or, in the event that aplurality of bearings are tagged with radioactive material, the individual bearing experiencing wearthrough of the overlying untagged silver layer can be identified by suitable detection means.

A further object of this invention is to provide for the electrodeposition of a layer of silver which includes at least one radioactive element in amounts which are insufficient to alter the properties or impair the quality of the silver layer, when it functions as part of the silver lining of an antifriction bearing.

Still a further object of the invention is to provide novel silver plating baths for accomplishing the above object.

Other and more specific related objects of the invention will be apparent from a study of the accompanying drawings and their description, it being understood that these are offered by way of example only and not in limitation of the invention, the scope of which is defined by the appended claims rather than by any preceding description.

In the drawings:

FIG. 1 is a schematic view partially in perspective of a bearing embodying the invention;

FIG. 2 is a view in section taken on plane 2-2 of FIG. 1;

FIG. 3 is an enlarged view ofa portion of FIG. 2; and

FIG. 4 is a schematic view of an arrangement showing the manner in which a plurality of bearings are monitored.

Referring first to FIG. 1, there is illustrated a bearing assembly comprising an outer race 12 and a cage 14 in which balls 16 or other antifriction devices are supported. An inner race 20 completes the conventional bearing structure shown by way of illustration. Oil or other fluent lubricant is supplied to the bearing 10 by way of a conduit 22 and is discharged from the bearing by way of a conduit 24. The oil discharged from the bearing contains particles and solid debris formed as the bearing wears away in service. The dirtylubricant is conducted to a detection apparatus containing a Geiger-Muller detector or other means for detecting the presence of radioactive particles when they are present in the lubricant leaving the bearing and containing a means for producing a signal 32 to signify the presence of such radioactive particles in the lubricant.

The lubricant leaves the detector 30 by way of conduit 28 and returns to inlet 22, after being filtered or otherwise processed to render it suitable for use in the bearing 10.

The annular bearing retainer or cage 14 shown in greater detail in FIGS. 2 and 3 includes an electrodeposited layer of silver or silver base alloy, an extremely thin film 42 of silver deposit containing a very small amount of a radioactive material which is situated in the lands or riding surface of the bearing cage, and

an overlying wear layer 44 of silver, deposited to a suitable thickness as a covering on radioactive film 42. The lands are selected only by way of example. For actual applications, other surfaces may be selected as they may be deemed to be more significant wear areas.

In service, layer 44 wears away and the wear particles being non-radioactive do not cause detector 30 and signal producing means 32 to issue any alarm.

When layer 44 has completely worn away, the particles worn from film 42 are detected by detector 30 and a signal is produced alerting the user to the fact that wear has proceeded through layer 44.

Continued use of the bearing in service leads to wear of layer 40, until such time as the bearing is replaced.

By way of illustration, layer 40 is a layer of silver approximately 0.0001 to 0.0003 inch thick deposited on the retainer 14 in the usual way, e.g., in accordance with AMS 2410, which for a steel base involves the sequential application of a nickel strike, a silver strike and then the silver plate to the thickness of 0.0001 to 0.0003 inch. The thickness of layer 40 is usually in proportion of the specification of the total thickness of bearing silver lining which in the above example is assumed'to be 0.001 inch.

The nickel strike and silver strike and silver plate are deposited on the base metal in that order from conventional baths well known in the art and are not believed to require further description. In the silver strike bath, the silver may be present in concentrations approximately 20 grams/liter and in the plating bath silver concentrations of about 100 grams/liter are commonly used. Cyanide baths are preferred, but other baths may be used at this stage of the process without affecting the results.

These concentrations are considerably larger than those utilized in the infinite dilution solution from which the thin radioactive layer 42 of silver is deposited onto the lands"of the silver-plated retainer 14.

After deposition of layer 40, and subsequent selective masking, the unmasked area, or layer 42, was plated from a cyanide bath containing radioactive cobalt-60 as a cobalt ammonium complex and radioactive silver-1 m as silver cyanide whereby a radioactive material comprising approximately 99% Ag and 1% Co was electrodeposited on the silvei piate't'ciathickness of 0.000005 inch, after which a layer of nonradioactive silver of 0.000005 inch thickness was flashed onto the radioactive layer to serve as a protective and buffer coating of the radioactive layer against the subsequent demasking and cleaning procedures, after which a 0.0005 inch thick layer of silver was deposited by electroplating from a conventional silver cyanide bath onto the entire bearing retainer surface, thus covering the radioactive material, and bringing the silver plate thickness to 0.001 inch.

The bath fro rn 't'viiiEifrTr? radioactive cobalt-60 tagged silver layer 42 was deposited on the unmasked areas of the bearing was prepared as follows:

One liter of deionized water was poured into a beaker. Twenty grams of KCN was added to the water and the mixture was stirred until dissolved with gentle heat (ll80F). While maintaining the heat, 7.4 grams of finely powdered cobaltous carbonate was added to the solution and dissolved therein. The liquid turned dark green and some sediment formed on the bottom of the beaker. To the resulting solution a solution of 10 milliliters of Nl-LOH, 1 gram of benzoic acid and 2 grams of salicylic acid were added in order to form cobalt ammonium complex ions, in situ. The formation of these ions was evidenced by a color change from greenish to reddish hue. The yield of cobalt as complexed cobalt ammonium was about 3.8 grams.

After repeated filtration, a 50 ml aliquot was withdrawn from the filtrate and run into a large evaporating pan, maintained at 180 to 200F, until the liquid was removed. The dessicated, dried salts were then packaged in a quartz tube and subjected to neutron bombardment to convert a portion of the cobalt to Co-60. The resulting cobalt ammonium compound, now tagged with Co-60, was readily redissolved in 1,050 ml of water in which it redissociated to the complex cobalt ammonium ion.

An auxiliary bath of radioactive silver-l 10m was prepared in similar fashion by neutron activation of the silver in AgCN.

A plating bath was now prepared by mixing 1 ml (0.7 mg of silver) of the Ag-l 10 m stock solution and 20 ml of a AgCN solution (containing 60 mg Ag) into the 1,050 ml solution containing the cobalt ammonium ions.

After the usual silver strike had been deposited on the base material, the cobalt-60 tagged silver-m tagged bath was used as the electrolyte and a radioactive layer of between 0000002 and 0.000005 inch was deposited on the non-radioactive (0.0001 0.0003 inch) silver layer.

Thereafter a layer of non-radioactive silver was plated over the entire surface to the depth desired for wear purposes (eg about 0.001 inch).

For the radioactive bath, concentrations of silver, cobalt, and potassium cyanide with appertinent specific activities within the following ranges have been found to be suitable for producing radioactive films having a radioisotope constituency of about 0.5 MG Co-60 and 0.5 no Ag-l 10m.

Concentration Specific Activity Ag (as CN) 3050 mg/liter l ac/mg Co (as Co(NH,)

complex) -250 mg/liter l00-l50 #c/mg KCN 50-l00 mg/liter amounts of cobalt-60 and silver-l lOm.

As is known, unless elaborate precautions are taken and ultrapure reagents and silver electrodes are utilized, electrodeposits of silver will contain small amounts of metallic impurities. The usual impurities are iron, copper or lead. It is well known that the presence of these metals in minute amounts do not disqualify the silver electrodeposit from normal service as a bearing silver lining. This "prior art" knowledge is the basis for a further embodiment of the present invenuon.

. TABLE I Specimen unmasked Anode to Bath activity surface cathode Bath composition(mg.) Bath Volt- Amp area Plating surface -volume Co Ag age erage (cathode) time area Co CN Ag (mL) (me) e) (volts) (ma) (sq. inch) (min.) radius Relative activity .m. p Plate activity Plate composi- Co at Ag at (uc) tion weight) Hydrogen 1. 17 .657 Plate weight Plate thickevolution mev. peak mev. peak Co Ag Co Ag (micrograms) ness (inches) Moderate 8000 27000 0.6 0.5 0.9 99.1 735 5 X 10- Moderate 7000 31000 0.5 0.6 0.7 99.3 841 5 X 10- Brisk 1600 52000 Very 500 1500 0.03 0.03 2.0 98 0 27 2 X 10- slight. Moderate... 2000 50000 0.15 0.92 0.2 99.8 867 5 X 10" G Brisk 2000 50000 0.15 0.92 0.2 99.8 867 5 X 10- mm was mamrial we vas tsii s wi l In a wear detection system applied to a plurality of bearings or a plurality of wear sites in a single bearing. each of the bearings or individual wear sites is tagged with radioisotopes which can be electrocodeposited with silver as impurity traces in amounts sufficiently small so as not to affect the quality or bond strength of the silver lining when it functions as an antifriction bearing silver lining. As there is a paucity of long-lived radioisotopes satisfying these requirements and as there is a need for distinguishing the silver wear from amongst a plurality of silver-lined articles assembled in a system, it is advantageous to have the tag invested in the silver lining comprise a dual radioisotope tag. This tag can consist of long-lived cobalt-6O (5.3 year halflife), which extends the useful detection period of the radioactively tagged silver lined article, and a radioisotope such as silver-l 10m, gold-195, zinc-65, antimony- 125, cadmium-109, or ruthenium-106, which serves to identify the radioactively tagged silver lined article. Further, this dual radioisotope tag permits eclectic uti-' lization of the best properties of available nuclear radiation detectors. Thus, a duo-detection system is established corresponding to the dual radioisotope tag whereby the simple, portable, and environmentally rugged Geiger-Mueller detector which is not capable of discriminating between radioactive species can be used, by virtue of the presence of cobalt-60, to monitor in-situ over an extended period of time the wear efflux from silver lined articles such monitoring would be frustrated were the shorter-lived identifier radioisotopes used singly while a scintillation crystal detector which is unsuitable for in-situ monitoring because of its fragility and environmental sensitivity is used as a secondary detector in the laboratory to corroborate the Geiger-Mueller signal as well as identify the secondary radioisotope such as silver-110m, gold-195, or other suitable radioisotopes, even after 5 years, being able to do so by virtue of its vastly superior detector sensitivity and the fact that the exigency of a rapid detection period as is requisite for in-situ monitoring is obviated by the need to corroborate the first signal as well as to identify the particular silver-lined bearing in distress.

In FIG. 4, the detection system shown schematically detects wear from six bearings tagged with the following combinations of radioisotopes:

cobalt-60, silver-1 10m cobalt-60, gold-195 cobalt-60, zinc-65 cobalt-60, antimony-125 cobalt-60, cadmium-109 cobalt-60, ruthenium-106 After the wear to the radioactively tagged silver layer has been detected by a Geiger-Mueller detector, used lubricant or the oil filter may be sampled and sent to a scintillation crystal detector which will analyze the sample for radioisotope constituency, identify the radioisotope and thus identify the specific bearing indicating distress.

The general plating process for incorporating a dual radioisotope tag of cobaltand Radioisotope A, which is any of the acceptable identifier radioisotopes such as gold-165, zincor others noted above is as follows:

Step 1. Bearing retainers silver plate is electrochemically stripped clean without removing base metal.

Step 2. Entire retainer surface is preliminarily preplated with silver layer 40 to desired depth or thickness.

Step 3. Retainer is masked and selectively cleaned of mask at bearing surface sites; preferred mask is beeswax.

Step 4. Retainer is mechanically scrubbed at the exposed surfaces to remove the superficial surface layers. This is done immediately prior to its immersion in the silver strike solutions. A quick jet stream wash precedes immersion. (Nylon wool is excellent for the mechanical scrubbing operation.)

Step 5. Retainer is immersed in cobalt-60 tagged cobalt-doped silver strike solution for 30 minutes.

Voltage setting: 2-6 volts Amperage setting: 30-200 milliamperes The plating thickness of deposited layer 42 will be approximately 0.000005 inch.

Step 6. Retainer is withdrawn and immersed in radioisotope A tagged silver. strike solution for 30 minutes. There is no rinse between withdrawal and immersion. Voltage and amperage requirements will be the same as those in Step 5. (This silver strike infinite dilution" solution is similar to that for the cobalt, except that a cyanic compound of radioisotope A is substituted in lieu of the cobalt salts.)

Step 7. Retainer is withdrawn and immersed in a nonradioactive silver strike solution for 30 minutes. Voltage and amperage requirements will be the same as those in Step 5. The purpose of this step is to provide the radioactive layer with a protective coating for the rigorous demasking and cleaning operations that follow.

Step 8. Retainer is withdrawn by remote handling equipment and vigorously rinsed, then dried by a jet of inert gas.

Step 9. Retainer is vapor degreased and cleaned.

Step 10. Retainer is overplated over entire surface with silver to thickness of 0.001 inch (layer 44).

Step 1 l. Retainer is heat-treated and tested in conformance with AMS 2410 or AMS 2412, depending on whether the base metal is steel or bronze, and is either accepted or rejected. If retainer is rejected, the cycle is repeated.

I claim:

1. A bearing comprising a metal base portion, a thin first layer of silver coated on said metal base, a thick second layer of silver constituting the main bearing wear surface and an extremely thin intermediate layer I of silver sandwiched between said first and said second bearing properties, and the amount of said radioactive atom species embedded in said extremely thin intermediate layer being insufficient to affect the bearing properties of the silver intermediate layer when it functions as an antifriction bearing; and yet being an amount sufficient to be detected in the silver wear particles carried away by a lubricant.

2. The bearing of claim 1 wherein the dopant in said intermediate layer of silver is cobalt-60.

3. The bearing of claim 2 wherein the dopant includes both cobalt-60 and at least one other radioactive species comprising a metal'which is compatible with the bearing function to be performed by the silver.

4. The bearing of claim 3 wherein said metal is selected from the group consisting of silver-l 10m, goldl95, zinc-65, antimony-l25, cadmium-109 and ruthenium- 106.

5. The bearing of claim 4 in which the bearing contains a plurality of wear sites each of which is tagged with a different radioactive atom species.

6. The bearing of claim 1 in combination with a detector, a means for applying a lubricant to the wearing portions of said bearing and a means for conveying the lubricant and the wear particles from said bearing to said detector whereby the presence of said radioactive atom species in said lubricant is detected as lubricant emerges from said bearing.

7. The bearing of claim 6 including two detectors, one of which detects the presence of cobalt-6O and another of which detects a second radioactive species.

8. The bearing of claim 1 in which the first layer is approximately 0.0001 inch, the intermediate layer is approximately 0.000005 inch and the third layer is approximately 0.001 inch. 

2. The bearing of claim 1 wherein the dopant in said intermediate layer of silver is cobalt-60.
 3. The bearing of claim 2 wherein the dopant includes both cobalt-60 and at least one other radioactive species comprising a metal which is compatible with the bearing function to be performed by the silver.
 4. The bearing of claim 3 wherein said metal is selected from the group consisting of silver-110m, gold-195, zinc-65, antimony-125, cadmium-109 and ruthenium-106.
 5. The bearing of claim 4 in which the bearing contains a plurality of wear sites each of which is tagged with a different radioactive atom species.
 6. The bearing of claim 1 in combination with a detector, a means for applying a lubricant to the wearing portions of said bearing and a means for conveying the lubricant and the wear particles from said bearing to said detector whereby the presence of said radioactive atom species in said lubricant is detected as lubricant emerges from said bearing.
 7. The bearing of claim 6 including two detectors, one of which detects the presence of cobalt-60 and another of which detects a second radioactive species.
 8. The bearing of claim 1 in which the first layer is approximately 0.0001 inch, the intermediate layer is approximately 0.000005 inch and the third layer is approximately 0.001 inch. 